1. Field of the Invention
This invention relates to semiconductor devices with enhanced hole mobility.
2. Description of the Prior Art
A complementary field effect transistor which employs Si as a semiconductor material uses a p-type channel and an n-type channel, and utilizes the fact that the characteristics of switching currents by the gates thereof are reverse to each other. Accordingly, it has the advantage that a signal can be amplified without permitting any considerable current to flow through field effect transistors (hereinbelow, abbreviated to "FETs") and that a logic operation is possible with a very low power consumption. Most of present-day ICs (integrated circuits) in which logic circuits are built are semiconductor devices of this type. The operating speed of the element, however, is determined by the value of either lower one of hole and electron mobilities (respectively denoted by .mu..sub.h and .mu..sub.e). In case of Si, .mu..sub.h =480 cm.sup.2 V.sup.-1 sec.sup.-1 determines the speed of the element. In addition, a semiconductor material GaAs is higher in .mu..sub.e than Si and is deemed a material for the ultrahigh speed devices of the coming generation. Since, however, the hole mobility (.mu..sub.h) of this material is 300 cm.sup.2 V.sup.-1 sec.sup.-1 and is lower than that of Si, the high electron mobility being an advantage is not exploited in a practicable semiconductor device even when the semiconductor device of the complementary type is fabricated. Accordingly, the material cannot be fully utilized for semiconductor devices which will form the mainstream of ICs and LSIs (large scale integrated circuits).
High speed switching elements utilizing larger electron mobility of GaAs have heretofore been proposed, as exemplified by T. Mimura et al. "Japanese Journal of Applied Physics" vol. 19, L 225, 1980.